Hypersensitivity to food is a world-wide problem and its prevalence is increasing. IgE- mediated reactions to foods, particularly peanuts, are the most common cause of food induced anaphylaxis. Cross-linking of IgE antibody by specific epitopes on the surface of allergens is a prerequisite for triggering symptoms of peanut allergy. IgE epitopes are frequently categorized as linear or conformational epitopes. Although linear IgE-binding epitopes of peanut allergens have been defined, little is known about conformational IgE-binding epitopes. Recently, accumulating evidence points to importance of conformational IgE epitopes in peanut allergy. In the proposed studies, we will identify clinically relevant conformational IgE epitopes of the two most important peanut allergens, Ara h 2 and Ara h 6, and examine the impact of the identified epitopes on IgE binding and IgE/FceR1 cross-linking events. Aim 1 will identify clinically relevant conformational IgE epitopes of Ara h 2 and Ara h 6 by screening phage peptide display library with serum IgE from peanut allergic patients. The selected phage peptides will be analyzed for sequence homology with Ara h 2/ Ara h 6 protein sequences and mapped on the Ara h 2 and Ara h 6 monomer surface using three-dimensional structures. IgE recognition pattern of the identified epitopes will be determined among patients with varied clinical histories. Aim 2 will test the identified epitopes for their ability to inhibi IgE binding to folded native Ara h 2/6 and for their capacity to inhibit cross-linking of IgE/FceR1 by allergen on effector cells. This study is the first to propose to identify and functionally characterize clinically important conformational IgE epitopes of the two most important peanut allergens. A better understanding of potential allergy-causing epitopes would lead to improved therapeutic strategies and better monitoring of immune-therapeutic interventions.